This invention relates to image plane registration systems, and more particularly to methods and apparatus for minimizing color fringing and image banding and registering multiple LED bar imagers to form a single image on a photoreceptor in an image-on-image system.
In electrophotographic systems, a photoreceptor may be supported by a mechanical carrier such as a drum or a belt. The photoreceptor may be charged to a generally uniform charge by subjecting the photoreceptor to a suitable charging device. The charge distribution on the photoreceptor may then be altered by the application of radiation, e.g., a laser, to the surface of the photoreceptor. Toner may then be attracted to the photoreceptor in a pattern consistent with the charge distribution on the photoreceptor.
Monochrome printers produce a hard copy in one toner color, typically black, and the copy may be made in a single pass of the charging device and toner source over the photoreceptor.
On the other hand, color printers use three primary colors, typically cyan, magenta and yellow, and in addition, optionally black. Several techniques have been developed over the years to adapt electrophotographic techniques to use multiple colors.
An exemplary apparatus for making high quality color prints by electrophotography is discussed in U.S. Pat. No. 4,728,983. A single photoconductive drum is electrostatically charged, laser-scan exposed, and toner developed during one rotation. In successive rotations different colored images corresponding to color separation images are assembled in register on the drum. This assembled color image is transferred to a receptor sheet in a final rotation of the drum.
U.S. Pat. No. 6,456,309 to Vittorio et al. discloses an apparatus for color image registration based upon belt and raster output scanner synchronization. A laser source projects a laser beam onto a multifaceted rotating polygon that sweeps the beam into a scan line across a moving photoreceptor. A start-of-scan detector produces start-of-scan signals when the laser beam is in position to write a scan line. A belt sensor produces belt signals when indicia on the photoreceptor pass a reference position. A controller receives the belt signals and the start-of-scan and then adjusts the photoreceptors rotational velocity such that the belt signals are an integral multiple of the start-of-scan signals.
U.S. Pat. No. 4,731,622 further discloses a multicolor electrostatic plotter in which toner applicators of different colors are successively applied to portions of a medium by repeatedly driving and rewinding a portion of the medium past an image head and the plurality of toner applicators for charge and toner application to imprint multiple color rasterized images on the medium by the use of electronic circuitry. A reference track on the medium is imprinted during the first color pass and deviations are detected during successive color passes. The plotter electronically adjusts the input data from a remote rasterizer by an amount equal to the substantially instantaneous offset so that lines of raster data are shifted by an amount substantially equal to the instantaneous displacement of the medium prior to charging the particular electrodes on the image head corresponding to the charge patterns for the next successive particular lines of raster information which are to be imprinted for the particular color image.
Each of the foregoing references is incorporated by reference in its entirety.